Hi JayJay,
I’d be happy to make a recommendation but, if you don’t mind me asking, about how tall is your partner, and about how much does she weigh (if you don’t know exactly, I would mainly just need to know if she’s under 120 lbs, between 120-180 lbs, between 180-260 lbs, or 260 lbs and up).
Regarding component suppliers for a possible DIY, while not inclusive, there are some options listed here but I don’t have records of the individual component suppliers. You can do also do a search like the one linked here and look for some other lists that have been discussed throughout the forum. I would point out that the attempt to design your own mattress with no real understanding of how the componentry will eventually “mesh” together to create overall comfort and may have in some cases higher costs and unintended results …so a tempering of expectations is always realistic.
Creating a DIY mattress out of separate components that are purchased from one or several different sources, I would refer you to post #15 here and the posts it links to (as well as options #1 and #2) so that you have more realistic expectations
Let us know which direction you wish to go into and we’ll do our best to guide you or answer your questions.
LMF